Particle System is floating in the air and not on the surface
The reason why your grass is not where it should be is that the object's origin is way off from the mesh, -30.5 m in X direction, 3.1 m in Y direction and 0.4 m in Z direction. That's the reason why they are not close to the surface or sometimes sinking in, because they are &quot;growing&quot; more than 30 m away from where they are &quot;born&quot;.

To get them distributed correctly you should set the origin close to the bottom of the grass mesh (image below). One way to do it: go to Edit Mode, select the bottom vertices of the grass, Shift+S &gt; Cursor to Selected. Then back into Object Mode, right-click on the grass object, Set Origin &gt; Origin to 3D Cursor.